The ratio of black to red stamps that Kathy had was 5 : 2. The cost of each of the black stamps was $5 and the cost of each of the red stamps was $6. Kathy sold 20% of the black stamps and the total cost of the unsold stamps was $192. How many black stamps did she have left?
| |
Black stamps |
Red stamps |
| Before |
5 u |
2 u |
| Change |
- 1 u |
|
| After |
4 u |
2 u |
Number of black stamps sold
= 20% x 5 u
=
20100 x 5 u
= 1 u
| |
Black stamps |
Red stamps |
Total |
| Number |
4 u |
2 u |
|
| Value |
$5 |
$6 |
|
| Total value |
20 u |
12 u |
$192 |
Total cost of unsold stamps
= 20 u + 12 u
= 32 u
32 u = 192
1 u = 192 ÷ 32 = 6
Number of black stamps that Kathy had left
= 20 u
= 20 x 6
= 120
Answer(s): 120
